Method and apparatus for camera calibration using light source

Abstract

Apparatuses for camera calibration using a light source are provided, one of apparatus comprises, a n-light sources (n is 3 or more) which can be mounted on the camera, an actual coordinate computation processing unit which irradiates light to an image pickup surface being captured by the camera through the n-light sources to capture an image of an n-sided polygon made up of n-light spots formed on the image pickup surface, and analyses a degree of distortion on the n-sided screen to obtain n or more coordinate pairs obtained by matching the coordinates on the screen and the coordinates on an actual space and a calibration computation processing unit which receives the n or more coordinate pairs as input to convert a two-dimensional coordinate on the screen into a three-dimensional coordinate on the actual space.

What is claimed is: 
     
         1 . An apparatus for performing calibration on a camera using a light source, the apparatus comprising:
 n-light sources, n being three or more, which can be mounted on the camera;   at least one processor configured to perform the calibration by implementing:
 an actual coordinate computation processing unit which receives data of an image of an n-sided polygon made up of n-light spots formed on an image pickup surface, and analyzes a degree of distortion on an n-sided screen to obtain at least n coordinate pairs obtained by matching coordinates on the n-sided screen and coordinates on an actual space; and 
 a calibration computation processing unit which receives the at least n coordinate pairs to convert a two-dimensional coordinate on the n-sided screen into a three-dimensional coordinate on the actual space. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the n is four, and
 the n-light sources are mounted in a form of a square so to have an optical axis parallel to an optical axis of the camera.   
     
     
         3 . The apparatus of  claim 2 , wherein, when the n-sided polygon is a rectangle on the image pickup surface and is a trapezoid on the n-sided screen, the actual coordinate computation processing unit determines that the camera is inclined with respect to the image pickup surface, and multiplies a length R 1 ′ from a center of the n-sided screen to an upper side of the trapezoid and a length R 2 ′ from the center of the n-sided screen to a lower side of the trapezoid by an angle per pixel of the camera to obtain an angle θ at which the camera is inclined in a vertical direction with respect to the image pickup surface, and wherein the length R 1 ′ and the length R 2 ′ are pixel lengths. 
     
     
         4 . The apparatus of  claim 3 , wherein the angle per pixel of the camera comprises at least one from among an angle per horizontal pixel obtained by dividing a horizontal angle of view of the camera by a horizontal resolution of the camera, and an angle per vertical pixel obtained by dividing a vertical angle of view of the camera by a vertical resolution of the camera. 
     
     
         5 . The apparatus of  claim 3 , wherein the actual coordinate computation processing unit obtains the angle θ by simultaneously setting tan (θ)=(Q+P)/H and tan (θ+θ1)=(2Q+P)/H and tan (θ−θ2)=P/H,
 wherein, θ1 is an angle from a center of the rectangle to a center of an upper side, θ2 is an angle from the center of the rectangle to a center of a lower side, Q is a half of a length of a long side of the rectangle, P is a distance on the image pickup surface from the lower side of the rectangle to a vertically lower point of the camera, and H is a height at which the camera is installed. 
 
     
     
         6 . The apparatus of  claim 3 , wherein the actual coordinate computation processing unit obtains the at least n coordinate pairs by matching the coordinates on the n-sided screen of four light spots forming the n-sided polygon and the coordinates on an image pickup plane in a one-to-one correspondence. 
     
     
         7 . The apparatus of  claim 2 , wherein the actual coordinate computation processing unit obtains a height H at which the camera is installed and an angle per pixel of the camera, when the n-sided polygon is a square on the image pickup surface and is a square on the n-sided screen, by determining the camera to be in a vertical direction with respect to the image pickup surface, and by utilizing a length R′ from a center of the n-sided screen to one side of the square and a half L′ of a resolution of the camera, and wherein the length R′ and the half L′ are pixel lengths. 
     
     
         8 . The apparatus of  claim 2 , wherein the at least one processor is further configured to implement:
 a camera mode control unit wherein, when the n-sided polygon is not a trapezoid on the n-sided screen, determines that there is an obstacle on the image pickup surface or the image pickup surface is not flat, and determines that the calibration is not performed.   
     
     
         9 . The apparatus of  claim 8 , wherein the at least one processor is further configured to implement:
 a light source control unit which equally rotates four light sources by θ t  to correct the n-sided polygon so as to be displayed in a trapezoidal shape on the n-sided screen, when the camera mode control unit determines that the calibration is not being executed.   
     
     
         10 . The apparatus of  claim 9 , wherein the camera mode control unit determines again to perform the calibration when the light source control unit corrects a rectangle to be displayed as the trapezoidal shape on the n-sided screen, and
 the actual coordinate computation processing unit analyzes the degree of distortion on the n-sided screen of the n-sided polygon, further using a rotation angle θt of a laser diode, and obtains the at least n coordinate pairs.   
     
     
         11 . The apparatus of  claim 1 , wherein the at least one processor is further configured to implement:
 a camera mode control unit which periodically repeats the calibration in accordance with a preset period.   
     
     
         12 . The apparatus of  claim 1 , wherein the at least one processor is further configured to implement:
 a light source control unit which analyzes a color of the image pickup surface to change colors of the n-light sources to colors that are complementary colors of the color of the image pickup surface.   
     
     
         13 . A non-transitory machine readable medium storing a program which when executed by at least one processor provides instructions for calibrating a camera, the instructions comprising:
 control a light emitting unit including n-light sources and being mounted to the camera, to project n-light spots on an image pickup surface;   capturing an image of an n-sided polygon formed by the n-light spots projected on the image pickup surface;   determining a degree of distortion on an n-sided screen to obtain at least n coordinate pairs obtained by matching coordinates on the n-sided screen and coordinates on an actual space; and   converting a two-dimensional coordinate on the n-sided screen into a three-dimensional coordinate on the actual space using the at least n coordinate pairs.